for National Geographic News
Microscopic crystals called quantum dots, which measure less than a millionth of a meter wide, might soon replace technology that has existed largely unchanged since 1879the incandescent lightbulb.
New research shows that applying a thin layer of these dots over light emitting diodes (LEDs) causes the diodes to emit white light with the warm hue of a typical household bulb.
The work might be the final step in helping replace today's incandescent bulbs with LEDs, which can last longer and use much less electricity.
The breakthrough discovery was made by 26-year-old chemistry graduate student Michael Bowers of Vanderbilt University in Nashville, Tennessee.
"We didn't set out to make a white-light LED. It happened by accident," said Sandra Rosenthal, the Vanderbilt associate professor who oversees Bowers' work.
Bowers and Rosenthal, along with fellow graduate student James McBride, describe their find in the October 18 issue of the Journal of the American Chemical Society.
The discovery started out as a favor for a friend. Bowers is the Vanderbilt chemistry department's resident quantum-dot chef. His job is to work up batches of the tiny crystals for researchers in the department to use.
McBride asked Bowers to produce a batch of quantum dots that were smaller than ones he had ever made before. McBride was interested in the relationship between the size and shape of nanocrystals and the types of energy they emit when stimulated.
Bowers made the dots by injecting molecules of the metals cadmium and selenide with a hot solvent, a chemical that loosens the metals' atoms so that bits break off and join into small clumps to form crystals.
After Bowers produced the crystals, he was curious to see what kind of light his newly minted dots would emit when a laser passed through them. He was surprised at the results.
"I expected [the light] to be blue or violet, but what came out was white," Bowers said. "I said, I've got to get a picture of this, because I may never be able to reproduce this."
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